1. Field of the Invention
The present invention relates generally to a charge transfer circuit for capacitive sensing and, more particularly, to a charge transfer circuit for capacitive sensing using active output voltage feedback (AVF) technology, which is insensitive to parasitic capacitance.
2. Description of the Related Art
Since capacitive sensors, such as touch screen panels (TSPs), have more advantages than other input devices, such as keyboards and mouses, they have become popular and have spread rapidly, especially in mobile systems. Capacitive sensors, such as touch input devices, provide effective and interactive input functions, such as a multi-touch function, a proximity sensing function, and a pattern input function. Furthermore, capacitive sensors are widely used for various application apparatuses for moisture sensing, bio-sensing and special purpose sensing, etc.
Recently, the sizes of display units have increased in many mobile application apparatuses, and thus display units require more touch points in order to achieve higher resolution. Electrodes generally formed of Indium Tin Oxide (ITO) in touch screen panels contain parasitic elements, such as capacitance and resistance, and these parasitic elements may incur reductions in performance in terms of both touch sensitivity and accuracy.
In order to reduce a parasitic effect, a discrete time integrators may be used as a capacitive sensor. However, since the capacitance of a touch screen panel decreases only in a touch state, a discrete time integrator uses only half of a supply voltage, and thus touch sensitivity is deteriorated.